As disclosed in JP 2012-070577 A (corresponding to US 2013/0082663 A1), a discharge system discharges DC power stored in a battery of an electric vehicle to an external device. The discharge system disclosed in JP 2012-070577 A is made for improving a safety of power discharge.
The above discharge system includes an electric vehicle equipped with a battery unit and a discharge apparatus that discharges the power stored in the battery unit of the electric vehicle. In the electric vehicle, two switches are disposed in respective power lines and two switching elements are also disposed in respective power lines. Each power line connects a connector to which the discharge apparatus is connected with the battery unit. Each switch switches on the power line according to a permit signal transmitted from the discharge apparatus or a permit signal transmitted from the battery management unit. Each switching element regulates a current that flows through the power line while the battery unit discharges the stored power.
The above discharge system supplies the DC power stored in the battery to the external device. Thus, the DC power output from the battery needs to be converted to AC power using an external inverter that is positioned outside of the vehicle. Accordingly, in the discharge apparatus positioned outside of the vehicle, an inverter needs to be included in a power converter of the discharge apparatus. JP 2012-070577 A does not mention anything about a use of the AC power output from the power converter of the discharge apparatus.
Suppose that the electric vehicle is equipped with an inverter for supplying converted AC power to an external device. In this kind of vehicle, the vehicle battery is charged by a DC power converted from the commercial power, and the DC power stored in the vehicle battery is converted to AC power by the internal inverter and is supplied to the external device. However, the AC power output from the electric vehicle may reversely flow through a power charging path instead of a power discharging path, and the reverse current may adversely affect a stability of the commercial power source, which is also known as a grid power system.